Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Mechanical and Materials Engineering


George K. Knopf

Second Advisor

Dr. M. Ostojic

Third Advisor

Dr. S. Nikumb


Lab-on-a-chip devices play an important role in a variety of applications such as analyzing DNA and RNA, medical screening, monitoring the environment, and chemical analysis. Often these devices must be disposable because they can only be used once to avoid sample contaminations. The cost of unit microfluidic devices then becomes a critical factor of the commercial success of the devices. These devices are typically produced using conventional microfabrication techniques such as photolithography and electroplating, which involve harmful chemicals extensively. Electroplating process typically requires long plating hours to reach the required thickness. To address these practical needs of fabricating inexpensive disposable devices, the ability to fabricate micromold masters for replication of polymeric microfluidic devices rapidly and with greener fabrication technologies is necessary. This dissertation illustrates new approaches to fabricate micromold masters based on non-lithographic processes and the minimal usage of chemicals. This thesis is organized into two major parts. The first part described the microfabrication technologies developed to manufacture micromold masters for replicating low cost disposable polymer microfluidic devices. Three methods were developed and laser was employed to fabricate the mask having microfluidic network patterns on a thin metallic sheet. The pattern on this mask was transferred onto a substrate to create the master. Three techniques to transfer the mask pattern onto the mold master substrates have been explored including the laser microwelding, micro-spark erosion, and partial hot embossing (hot intrusion) process. The method that required the use of the laser welding is termed as Laser Cutting, laser Welding, and Molding (LCWM). The method that required the use of the microspark erosion to remove materials in order to produce the master is termed as Laser cutting, Electro-Discharging, and Molding (LEDM ). The method that employed the partial hot embossing process to create the polymeric mold masters is termed as Laser cutting, Hot embossing, and Molding (LHEM). Proof-of-concept demonstrations of these three methods were experimentally validated. Each method has its unique advantages and

disadvantages and the selection of the developed methods used in fabrication of micromold masters depends on the requirements of the intended application. The second part of this dissertation described the further investigations of the LHEM method because of its fabrication simplicity, rapid process, and produced high quality surface finishes. An extensive series of experimentations and analysis were conducted. Subsequently, an empirical model was derived to characterize the experimental observations. A finite element method (FEM) model was also developed to gain further understanding of the hot intrusion process. The FEM predictions were in good agreements with the experimental data. Both experimental data and FEM analysis reveal a strong positive correlation between the extruded height and width of cross- sectional extruded microreliefs created by the hot intrusion. This correlation, if employed innovatively, enables us to fabricate 3D microfeatures. Several examples including a 3D micronozzle were demonstrated.



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